1. Field
The present disclosure is directed to additive compositions and lubricating oils containing particular imide or amide groups. In particular, it is directed to additive compositions and lubricating oils containing particular imides, amides, or salts thereof as friction modifiers for reducing one or both of thin film friction and boundary layer friction.
2. Description of the Related Technology
To ensure smooth operation of engines, engine oils play an important role in lubricating a variety of sliding parts in the engine, for example, piston rings/cylinder liners, bearings of crankshafts and connecting rods, valve mechanisms including cams and valve lifters, and the like. Engine oils may also play a role in cooling the inside of an engine and dispersing combustion products. Further possible functions of engine oils may include preventing or reducing rust and corrosion.
The principle consideration for engine oils is to prevent wear and seizure of parts in the engine. Lubricated engine parts are mostly in a state of fluid lubrication, but valve systems and top and bottom dead centers of pistons are likely to be in a state of boundary lubrication. The friction between these parts in the engine may cause significant energy losses and thereby reduce fuel efficiency. Many types of friction modifiers have been used in engine oils to decrease frictional energy losses.
Improved fuel efficiency may be achieved when friction between engine parts is reduced. Thin-film friction is the friction generated by a fluid, such as a lubricant, moving between two surfaces, when the distance between the two surfaces is very small. It is known that some additives normally present in engine oils form films of different thicknesses, which can have an effect on thin-film friction. Some additives, such as zinc dialkyldithio phosphate (ZDDP) are known to increase thin-film friction. Though such additives may be required for other reasons such as to protect engine parts, the increase in thin-film friction caused by such additives can be detrimental.
Reducing boundary layer friction in engines may also enhance fuel efficiency. The motion of contacting surfaces in an engine may be retarded by boundary layer friction. Non-nitrogen-containing, nitrogen-containing, and molybdenum-containing friction modifiers are sometimes used to reduce boundary layer friction.
U.S. Pat. No. 6,232,275 discloses a lubricating oil composition for an automatic transmission. The composition comprises a succinic acid amide represented by the formula:
where R1 is an alkyl group or an alkenyl group having 5 to 250 carbon atoms, and m is an integer from 0 to 6. R1 is preferably a polybutenyl group or a polyisoybutenyl group in particular. Optional components in the disclosed lubricating oil composition may be selected from viscosity index improvers, antioxidants, metal deactivators, defoaming agents, detergents, extreme pressure agents and rust preventives.
U.S. Pat. No. 5,122,616 discloses succinimides that function as fuel detergents useful for engines. The succinimides are represented by the formula:
where R is an alkylene of 2 to 4 carbon atoms, R′ is a substantially straight chain alkyl or alkenyl group averaging at least 12 but less than 30 and preferably at least 14 but no more than 28 carbon atoms, R″ is a hydrogen atom or an alkyl of 1 to 5 carbon atoms, and n is an integer in the range of 1 to 10.
U.S. Pat. No. 4,338,206 discloses a lubricating oil for engines that contains a quaternary ammonium succinimide salt having the formula:
in which R is a hydrocarbyl radical having from 25 to 200 carbon atoms, R1 is a divalent hydrocarbon radical having from 1 to 10 carbon atoms, R2 is a hydrocarbyl radical having from 1 to 10 carbon atoms, n has a value of 0 or 1, and X is a halide radical. Other additives such as standard pour depressants, viscosity index improvers, anti-foaming agents and supplementary detergent-dispersants may also be included in the lubricating oil.
U.S. Pat. No. 8,093,191 discloses an engine lubricant containing a succinimide with the structure:
where each R1 is independently an alkyl group, frequently a polyisobutene group with a molecular weight of 500-5000, and R2 is an alkylene group, commonly ethylene groups. Additional components in the lubricant may include antioxidants and anti-wear agents.
EP 2450423 A1 discloses a water-based lubricant for plastic working, comprising a resin component containing a copolymer or homopolymer of monomers having an ethylenically unsaturated bond, including at least maleic anhydride (A), an inorganic component (B), and a solid lubricating component (C), wherein the solid lubricating component (C) is soft and slippery itself and has the function of reducing frictional force between dies and works during plastic working. Amino acid derivatives that have a hydrocarbon group with 11 or more carbon atoms in the molecular structure may be used as component (C). A specific example may be N-lauroyl-L-lysine.
In recent years there has been a growing desire to employ lubricating oils to provide higher energy-efficiency, especially lubricating oils that reduce friction. The present disclosure provides improved lubricating oils that may reduce one or both of thin film friction and boundary layer friction.